GW151226 was a gravitational wave signal detected by the LIGO observatory on 25 December 2015 local time (26 Dec 2015 UTC).

[1] Analysis indicated the signal resulted from the coalescence of two black holes with 14.2+8.3−3.7 and 7.5+2.3−2.3 times the mass of the Sun, at a distance of 440+180−190 megaparsecs (1.4 billion light years) from Earth.

[1][3] In both of the first two black hole mergers analyzed, the mass converted to gravitational waves was roughly 4.6% of the initial total.

[1] The black holes were smaller than in the first detection event, which led to different timing for the final orbits and allowed LIGO to see more of the last stages before the black holes merged—55 cycles (27 orbits) over one second, with frequency increasing from 35 to 450 Hz, compared with only ten cycles over 0.2 second in the first event.

[1] The GW151226 event suggests that there is a large population of binary black holes in the Universe that will produce frequent mergers.